A radio frequency (RF) calibrating system and a method for calibrating RF power of communication devices are provided. The method collects RF signals transmitted from the communication devices, and generates a group of training samples by retrieving measurement data from the RF signals. The method further constructs a neural network according to the group of training samples, calibrate RF power of the communication devices using the neural network, and generate corresponding calibration results of the RF power. In addition, the method generates a frequency spectrum of the RF power according to the calibration results of the RF power, and displays the frequency spectrum on a display device of the RF calibrating system.